Need help with a plot hole

I'm writing something about some teens who are descendants of greek gods. I need a reason to keep the main character semi-involved with her human ex-boyfriend. I need there to still be feelings and some type of relationship but they can't be exclusive. What could be something that would tie her and her ex together, but not be so strong that she would be overly attached to him.

What if the MC has to leave her family behind and she asked the ex-boyfriend to watch over them. They still have feelings for each other, but he knows or understands why she had to leave even though she may not have told her family.

You probably already found a solution for this, but what if she finds out that her ex is also somehow part of the whole Greek god scene? Not that he's a descendant, but like he's fated to be a guardian of the children of the Gods. Or something. lol

My suggestion is that she's tied to her ex either because of something he did for her (she feels she owes him) or something she did to him (she feels guilty) It would be great if whatever he did or she did comes into play at a later point in the story. Good luck